The present invention relates to a method and arrangement for varying the exposed surface of an x-ray detection/registering means. The x-ray imaging apparatus comprises at least one x-ray source, a collimator having slots and a registering means.
When analysing an object, specially a tissue or a part of human body, through x-ray radiation, the result of the analyse depends highly on the number of x-rays passing through the object and registered by means of a detector or film. The thickness and density of different objects are some parameters that effect the passage of the x-rays. In for example mammography examination the x-ray apparatus must be adjusted for different patients having different bodily characteristics.
In case of an x-ray detector, one important parameter is the radiated area, i.e., the surface of the detector, which is exposed to the x-rays. Yet another important parameter is the time of exposure, which in case of living tissues is critical, as the radiation dose corresponding to a long exposure time for x-ray radiation may endanger the tissue by inducing cancer.
Semiconductor based x-ray detectors are known, e.g. through Swedish Patent Application No. 9801677-7, Danielsson. According to this document an edge-on detector is placed tilted with respect to the incident x-rays.
According to the pending Swedish patent application no. 9903559-4, an arrangement for detecting x-ray radiations is provided comprising a carrying member on one face arranged with detectors consisting of a plurality of sensors arranged on a substrate. The detectors are arranged substantially edge to edge at least in one row on at least one side of said carrying member.
U.S. Pat. No. 4,937,453, describes an apparatus for detecting x-ray radiation in a radiographic imaging context is disclosed. It is particularly useful in conjunction with slot and slot scan radiography. In accordance with this invention, detectors are constructed and arranged such that substantially all of the energy from an x-ray to be detected is discharged in the detector. In this way a detector is provided which provides a direct electronic read out, high x-ray stopping power and high spatial resolution while obtaining good signal collection efficiency without the use of excessively high voltage levels. In the preferred embodiment, solid-state x-ray detectors are constructed such that the thickness of the detector along the direction of incident X-rays is long enough that substantially all of the x-ray energy is discharged in the detector. The detector is arranged edge on, with its longitudinal axis substantially parallel to the incident x-ray.
Also, gas-based detectors are known. WO 99/23859, for example concerns an apparatus for radiography, and especially for planar beam radiography, and also a detector for detecting incident radiation. The detector according to this invention, which detects incident radiation, is a gaseous parallel plate avalanche chamber, including electrode arrangements between which a voltage is applied for creating an electrical field, which causes electron-ion avalanches of primary and secondary ionization electrons released by incident radiation. The detector is oriented, in relation to the incident radiation, so that the radiation enters sideways between a first and a second parallel plate, between which the electrical field is created. Electrical signals induced by said electron-ion avalanches are detected in at least one detector electrode arrangement, including a plurality of detector electrode elements arranged adjacent to each other, each along a direction being essentially parallel to the incident radiation.
U.S. Pat. No. 4,953,189 discloses a method and device for producing flux equalized x-ray images for medical radiography through the use of a scanning fan shaped x-ray beam and a feedback control system which regulates the beam intensity at a multiple number of points along the fan beam to compensate for the x-ray attenuation variations of the patient.
According to U.S. Pat. No. 5,136,672, at least one primary diaphragm comprises two elements displaceable so as to form a linear fan-shaped beam, which is incident on an object to be examined. The elements form the slit-shaped aperture forming the fan beam in their normal X-ray beam forming position and are moveable to a respective, selectable limit position perpendicularly to the fan shaped beam in order to define and mark an examination zone greater in cross-section area than the fan beam with a light beam. Light incident on the examination zone is restricted by the diaphragm elements in their limit positions, thus marking the examination zone with the light beam. X-ray exposure of the object to be examined takes place only when the elements are between the two positions defining the examination zone of the primary diaphragm where its diaphragm elements occupy in their respective limit positions.
The main object of the present invention is to provide a method and arrangement, which enable varying the number of detected x-rays, preferably depending on the features of the object to be examined.
Preferably, the invention is applicable in the applications using scanned slot set-up.
Another object of the invention is to adjust the spatial resolution to comply with the diagnostic requirements for the moment by varying the slot width.
Therefore the initially mentioned collimator arrangement comprises at least two substantially similar collimator parts having similar slot configurations arranged on top of each other and that said substantially similar collimator parts are arranged displaceable relative each other. According to one preferred embodiment, the slots of each collimator part are arranged displaced relative each other along a longitudinal axis of the collimator.
According to another embodiment said slots of each collimator part are arranged along a longitudinal axis of the collimator.
The registering means can be one of a semiconductor-based detector, a gas-based detector or an x-ray sensitive film.
In an x-ray imaging apparatus comprising at least one x-ray source, a collimator arrangement and a registering means, the collimator arrangement being provided for varying an exposure areas of said registering means to x-ray radiation from said x-ray source, the invention relates to a method for providing said variable exposure of said registering means. The method comprises providing said collimator arrangement with at least two substantially similar collimator parts having similar slot configurations and arranging said parts on top of each other displaceable relative each other.